Antiferromagnetic stabilized storage layers in GMRAM storage devices

ABSTRACT

A giant magnetoresistive memory device includes a magnetic sense layer, a magnetic storage layer, a non-magnetic spacer layer between the magnetic sense layer and the magnetic storage layer, and an antiferromagnetic layer formed in proximity to the magnetic storage layer. The antiferromagnetic layer couples magnetically in a controlled manner to the magnetic storage layer such that the magnetic storage layer has uniform and/or directional magnetization. Additionally or alternatively, an antiferromagnetic layer may be formed in proximity to the magnetic sense layer. The antiferromagnetic layer in proximity to the magnetic sense layer couples magnetically in a controlled manner to the magnetic sense layer such that the magnetic sense layer has uniform and/or directional magnetization.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a divisional of parent U.S. application Ser. No.10/706,068, filed Nov. 12, 2003.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The Government has rights in this invention pursuant to Contract No.DTRA01-00-C-002 awarded by the Defense Threat Reduction Agency.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a memory device that utilizesmagnetoresistance.

BACKGROUND OF THE INVENTION

A magnetoresistive (MR) device is a device whose resistance changes inaccordance with a change in magnetization. Almost every conductingmagnetic material exhibits some magnetoresistance. However, themagnetoresistive effect is particularly large in certain materials suchas permalloys, which are nickel-iron (NiFe) alloys, and otherferromagnetic materials such as Co, Ni, and Fe alloys. Magnetoresistivedevices respond to magnetic fields, and provide signals that typicallyare significantly more than that achieved with Hall sensors. A class ofmagnetoresistive devices with a larger sensitivity than standardmagnetoresistive devices is known as giant magnetoresistive (GMR)devices. A random access memory that uses magnetoresistive films isgenerally referred to as a magnetoresistive random access memory (MRAM).

In an MRAM, a triple-layer structure having two ferromagnetic layerstructures separated by a thin non-magnetic layer therebetween form abasic memory device. One of the ferromagnetic layer structures is usedto store (write) information and the other of the ferromagnetic layerstructures is used to sense (read) the stored information.

Typically, giant magnetoresistive devices are realized by choosing thethicknesses of the ferromagnetic thin-films and the intermediate layersin “sandwich” structures. Such devices, with the giant magnetoresistiveeffect, yield a magnetoresistive response that can be at least an orderof magnitude greater than that associated with anisotropicmagnetoresistive devices.

The magnetization of the ferromagnetic layers in giant magnetoresistivememories can be intended to be uniform. However, under certainconditions, the magnetization can become non-uniform. Thisnon-uniformity can reduce the repeatability of the switching that occursduring writing of information to the giant magnetoresistive devicewhich, in turn, reduces the reliability of the giant magnetoresistivememory.

The present invention is directed to an arrangement for increasing theuniformity of the magnetization of the ferromagnetic layers in giantmagnetoresistive memories.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a giantmagnetoresistive memory device comprises a magnetic storage layer, amagnetic sense layer, a non-magnetic spacer layer between the magneticsense layer and the magnetic storage layer, and an antiferromagneticlayer formed in proximity to the magnetic storage layer. Theantiferromagnetic layer couples magnetically in a controlled manner tothe magnetic storage layer such that the magnetic storage layer hasuniform and/or directional magnetization.

In accordance with another aspect of the present invention, a giantmagnetoresistive memory device comprises a magnetic storage layer, amagnetic sense layer, a non-magnetic spacer layer between the magneticsense layer and the magnetic storage layer, and first and secondantiferromagnetic layers. The first antiferromagnetic layer is formed inproximity to the magnetic storage layer whereby the firstantiferromagnetic layer couples magnetically in a controlled manner tothe magnetic storage layer such that the magnetic storage layer hasuniform and/or directional magnetization. The second antiferromagneticlayer is formed in proximity to the magnetic sense layer whereby thesecond antiferromagnetic layer couples magnetically in a controlledmanner to the magnetic sense layer such that the magnetic sense layerhas uniform and/or directional magnetization.

In accordance with still another aspect of the present invention, amethod of fabricating a giant magnetoresistive memory device comprisesthe following: forming a non-magnetic spacer layer between a magneticsense layer and a magnetic storage layer; and, forming anantiferromagnetic layer in proximity to one of the magnetic storagelayer and the magnetic sense layer whereby the antiferromagnetic layercouples magnetically in a controlled manner to the one of the magneticstorage layer and the magnetic sense layer such that the one of themagnetic storage layer and the magnetic sense layer has uniform and/ordirectional magnetization.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will become more apparent from adetailed consideration of the invention when taken in conjunction withthe drawings in which:

FIG. 1 illustrates the layers of a conventional multilayer stack usedfor giant magnetoresistive memories;

FIG. 2 illustrates the layers of a multilayer stack used for giantmagnetoresistive memories according to one embodiment of the presentinvention;

FIG. 3 illustrates the layers of a multilayer stack used for giantmagnetoresistive memories according to another embodiment of the presentinvention; and,

FIGS. 4-7 illustrate additional embodiments of the present invention.

DETAILED DESCRIPTION

As shown in FIG. 1, a giant magnetoresistive memory device 10 includes aseed layer 12 which may be formed, such as by sputter deposition ofsilicon nitride or tantalum, on a substrate 14. The substrate 14 may besilicon. The seed layer 12 is optional.

A storage layer 16 is formed over the seed layer 12. The storage layer16, for example, may be a ferromagnetic alloy or multilayer such asNiFeCo, NiFe/CoFe, NiFe, or CoFe that is sputter deposited over the seedlayer 12. The material, thickness, and layer structure is chosen tooptimize switching and magnetoresistive properties for writing and forreading. The storage layer 16 is used to store data stored in the giantmagnetoresistive memory device 10. Typically, the storage layer 16 has athickness of between 1 nm and 10 nm.

A non-magnetic, electrically conductive spacer layer 18 is formed overthe ferromagnetic storage layer 16. The non-magnetic, electricallyconductive spacer layer 18, for example, may be copper and may besputter deposited over the storage layer 16. Typically, for example, thenon-magnetic, electrically conductive spacer layer 18 has a thickness ofbetween 2 and 4 nm.

A sense layer 20 is formed over the non-magnetic, electricallyconductive spacer layer 18. The sense layer 20, for example, may be aferromagnetic alloy or multilayer such as NiFeCo, NiFe/CoFe, NiFe, orCoFe that is sputter deposited over the non-magnetic, electricallyconductive spacer layer 18. The sense layer 20 is used to read data fromthe giant magnetoresistive memory device 10. Typically, the sense layer20 has a thickness of between 1 nm and 10 nm.

As discussed above, the magnetization of the storage layer 16 may notalways be uniform or aligned in the proper direction. Thisnon-uniformity can reduce the repeatability of the switching that occursduring writing of information to the giant magnetoresistive memory cell10 which, in turn, reduces the reliability of the giant magnetoresistivememory device 10.

The arrangement of FIG. 2 results in more uniformity and directionalityof the magnetization in the storage layer 16.

As shown in FIG. 2, a giant magnetoresistive memory device 30 includes aseed layer 32 which may be formed such as by sputter deposition ofsilicon oxide(s), silicon nitride or tantalum on a substrate 34. Thesubstrate 34, for example, may be silicon. The seed layer 32 isoptional.

A storage layer 36 is formed over the seed layer 32. The storage layer36, for example, may be a ferromagnetic alloy or multilayer such asNiFeCo, NiFe/CoFe, NiFe, or CoFe that is sputter deposited on the seedlayer 32. The storage layer 36 is used to write data to the giantmagnetoresistive memory device 30. The storage layer 36 may have athickness, for example, of between 1 nm and 10 nm.

A non-magnetic, electrically conductive spacer layer 38 is formed overthe storage layer 36. For example, the non-magnetic, electricallyconductive spacer layer 38 may be copper and may be sputter depositedover the storage layer 36. The non-magnetic, electrically conductivespacer layer 38 may have a thickness, for example, of between 2 and 4nm.

A sense layer 40 is formed over the non-magnetic, electricallyconductive spacer layer 38. The sense layer 40, for example, may be aferromagnetic alloy or multilayer such as NiFeCo, NiFe/CoFe, NiFe, orCoFe that is sputter deposited over the non-magnetic, electricallyconductive spacer layer 38. The sense layer 40 is used to read data fromthe giant magnetoresistive memory device 30. The sense layer 40 may havea thickness, for example, of between 1 nm and 10 nm.

An antiferromagnetic layer 42 is formed over the seed layer so that theantiferromagnetic layer 42 is between the storage layer 36 and the seedlayer 32. The antiferromagnetic layer 42, for example, may be FeMn,PtMn, NiMn, or CrPtMn that is sputter deposited over the seed layer 32so that the antiferromagnetic layer 42 is between the storage layer 36and the seed layer 32. The antiferromagnetic layer 46 may have athickness, for example, of between 5 nm and 50 nm.

The antiferromagnetic layer 46 provides a controlled level of magneticcoupling to the storage layer 36. This controlled magnetic couplingtends to induce parallel and/or directional alignment of themagnetization in the storage layer 36 to improve switchingcharacteristics and thereby improve the magnetic properties andreliability of the giant magnetoresistive memory device 30. However, thecoupling should not be so strong as to significantly alter the switchingfields of the giant magnetoresistive memory device 30.

If desired, a cap-layer, for example made of Ta, may be suitably formedover the sense layer 40.

The arrangement of FIG. 3 also results in more uniformity of themagnetization in the storage layer 16, and in more uniformity of themagnetization in the sense layer 20.

As shown in FIG. 3, a giant magnetoresistive memory device 50 includes aseed layer 52 which may be formed such as by sputter deposition ofsilicon oxide(s), silicon nitride or tantalum on a substrate 54. Thesubstrate 54, for example, may be silicon. The seed layer 52 isoptional.

A first antiferromagnetic layer 56 is formed on the seed layer 52. Thefirst antiferromagnetic layer 56, for example, may be FeMn, PtMn, NiMn,or CrPtMn, that is sputter deposited over the seed layer 52. The firstantiferromagnetic layer 56 may have a thickness, for example, of between10 nm and 50 nm.

A storage layer 58 is formed over the first antiferromagnetic layer 56.The storage layer 58, for example, may be a ferromagnetic alloy ormultilayer such as NiFeCo, NiFe/CoFe, NiFe, or CoFe that is sputterdeposited over the first antiferromagnetic layer 56. The storage layer58 is used to store (write) data to the giant magnetoresistive memorydevice 50. The storage layer 58 may have a thickness, for example, ofbetween 1 nm and 10 nm.

A non-magnetic, electrically conductive spacer layer 60 is formed overthe storage layer 58. For example, the non-magnetic, electricallyconductive spacer layer 60 may be copper and may be sputter depositedover the storage layer 58. The non-magnetic, electrically conductivespacer layer 60 may have a thickness, for example, of between 2 nm and 4nm.

A sense layer 62 is formed over the non-magnetic, electricallyconductive spacer layer 60. The sense layer 62, for example, may be aferromagnetic alloy or multilayer such as NiFeCo, NiFe/CoFe, NiFe, orCoFe that is sputter deposited over the non-magnetic, electricallyconductive spacer layer 60. The sense layer 62 is used to read data fromthe giant magnetoresistive memory device 50. The sense layer 62 may havea thickness, for example, of between 1 nm and 10 nm.

A second antiferromagnetic layer 64 is formed over the sense layer 62.The second antiferromagnetic layer 64, for example, may be FeMn, PtMn,NiMn, or CrPtMn that is sputter deposited over the sense layer 62. Thesecond antiferromagnetic layer 68 may have a thickness, for example, ofbetween 10 nm and 50 nm.

The first antiferromagnetic layer 56 provides a controlled level ofmagnetic coupling to the storage layer 58. This controlled magneticcoupling tends to induce parallel and/or directional alignment of themagnetization in the storage layer 58 to improve magneticcharacteristics and thereby improve the magnetic properties andreliability of the giant magnetoresistive memory device 50.

Similarly, the second antiferromagnetic layer 64 provides a controlledlevel of magnetic coupling to the sense layer 62. This controlledmagnetic coupling tends to induce parallel and/or directional alignmentof the magnetization in the sense layer 62 also to improve magneticcharacteristics and thereby improve the magnetic properties andreliability of the giant magnetoresistive memory device 50. However, thecouplings as described above should not be so strong as to significantlyalter the switching fields of the giant magnetoresistive memory device50.

If desired, a cap-layer, for example made of Ta, may be suitably formedover the second antiferromagnetic layer 64.

Certain modifications of the present invention will occur to thosepracticing in the art of the present invention. For example, the layersshown in FIGS. 2 and 3 may be extended and patterned to form MRAMs.Also, electronics may be formed in the substrate 54 to aid in thestoring of information and the reading of that information.

Additionally, the giant magnetoresistive memory device 30 is shown inFIG. 2 as having a single antiferromagnetic layer 42 formed between thestorage layer 36 and the seed layer 32. Instead, two antiferromagneticlayers may be formed so that one antiferromagnetic layer is on each sideof the storage layer 36. For example, as shown in FIG. 4, a giantmagnetoresistive memory device 70 includes a seed layer 72 which may beformed on a substrate 74. An antiferromagnetic layer 76 is formed overthe seed layer 72, a storage layer 78 is formed over theantiferromagnetic layer 76, an antiferromagnetic layer 80 is formed overthe storage layer 78, a non-magnetic, electrically conductive spacerlayer 82 is formed over the antiferromagnetic layer 80, and a senselayer 84 is formed over the non-magnetic, electrically conductive spacerlayer 82. If desired, a cap-layer may be suitably formed over the senselayer 84.

Similarly, the giant magnetoresistive memory device 50 is shown in FIG.3 as having a single second antiferromagnetic layer 64 formed over thesense layer 62, and a single first antiferromagnetic layer 56 formedunder the storage layer 58. Instead, two antiferromagnetic layers may beformed so that one antiferromagnetic layer is on each side of senselayer 62, and two antiferromagnetic layers may be formed so that oneantiferromagnetic layer is on each side of storage layer 58. Forexample, as shown in FIG. 5, a giant magnetoresistive memory device 90includes a seed layer 92 which may be formed on a substrate 94. Anantiferromagnetic layer 96 is formed over the seed layer 92, a storagelayer 98 is formed over the antiferromagnetic layer 96, anantiferromagnetic layer 100 is formed over the storage layer 98, anon-magnetic, electrically conductive spacer layer 102 is formed overthe antiferromagnetic layer 100, an antiferromagnetic layer 104 isformed over the non-magnetic, electrically conductive spacer layer 102,a sense layer 106 is formed over the antiferromagnetic layer 104, and anantiferromagnetic layer 108 is formed over the sense layer 106. Ifdesired, a cap-layer may be suitably formed over the antiferromagneticlayer 108.

Moreover, the antiferromagnetic layers are shown above as being formedover and/or under their corresponding ferromagnetic layers. However, theantiferromagnetic layers instead may be formed either under or overtheir corresponding ferromagnetic layers. It is also possible to formlayers between the antiferromagnetic layers and their correspondingferromagnetic layers as long as the controlled magnetic couplingdescribed above is established to ensure substantially uniform and/ordirectional magnetization of the ferromagnetic layers.

As an example, FIG. 6 shows a giant magnetoresistive memory device 110that includes a seed layer 112 which may be formed on a substrate 114. Astorage layer 116 is formed over the seed layer 112, anantiferromagnetic layer 118 is formed over the storage layer 116, anon-magnetic, electrically conductive spacer layer 120 is formed overthe antiferromagnetic layer 118, and a sense layer 122 is formed overthe non-magnetic, electrically conductive spacer layer 120. If desired,a cap-layer may be suitably formed over the sense layer 122.

As another example, FIG. 7 shows a giant magnetoresistive memory device130 that includes a seed layer 132 formed on a substrate 134. A storagelayer 136 is formed over the seed layer 132, an antiferromagnetic layer138 is formed over the storage layer 136, a non-magnetic, electricallyconductive spacer layer 140 is formed over the antiferromagnetic layer138, an antiferromagnetic layer 142 is formed over the non-magnetic,electrically conductive spacer layer 140, and a sense layer 144 isformed over the antiferromagnetic layer 142. If desired, a cap-layer maybe suitably formed over the sense layer 144.

It should be noted that, when two antiferromagnetic layers are used perstorage and/or sense layer, the antiferromagnetic layer near thenon-magnetic spacer layer may be the thinner of the twoantiferromagnetic layers. However, this thinner antiferromagnetic layershould be thick enough to impart magnetization uniformity anddirectionality, but not so thick as to disrupt magnetoresistiveproperties.

Further, the strength of the antiferromagnetic coupling to a storagelayer may be different than that of the antiferromagnetic coupling to asense layer. First, this difference in coupling can be used to optimizeperformance. Second, when the antiferromagnetic coupling to the senselayer is substantial, the strongly coupled antiferromagnetic layer canbe used to fix or pin the magnetization of the sense layer. The couplingof the antiferromagnetic layer that is adjacent to the storage layer canbe adjusted, for example by choice of material or processing, to controluniformity and/or directionality of the magnetization in the storagelayer without necessarily significantly altering the switching fields ofthe storage layer.

Accordingly, the description of the present invention is to be construedas illustrative only and is for the purpose of teaching those skilled inthe art the best mode of carrying out the invention. The details may bevaried substantially without departing from the spirit of the invention,and the exclusive use of all modifications which are within the scope ofthe appended claims is reserved.

1-27. (canceled)
 28. A method of fabricating a giant magnetoresistivememory device comprising: forming a non-magnetic spacer layer between amagnetic sense layer and a magnetic storage layer; and, forming anantiferromagnetic layer in proximity to one of the magnetic storagelayer and the magnetic sense layer whereby the antiferromagnetic layercouples magnetically in a controlled manner to the one of the magneticstorage layer and the magnetic sense layer such that the one of themagnetic storage layer and the magnetic sense layer has uniform and/ordirectional magnetization.
 29. The method of claim 28 wherein themagnetic storage layer comprises a ferromagnetic alloy.
 30. The methodof claim 28 wherein the magnetic storage layer comprises ferromagneticmultilayers.
 31. The method of claim 28 wherein the magnetic sense layercomprises a ferromagnetic alloy.
 32. The method of claim 28 wherein themagnetic sense layer comprises ferromagnetic multilayers.
 33. The methodof claim 28 wherein the magnetic sense layer comprises a firstferromagnetic alloy, and wherein the magnetic storage layer comprises asecond ferromagnetic alloy.
 34. The method of claim 28 wherein themagnetic sense layer comprises first ferromagnetic multilayers, andwherein the magnetic storage layer comprises second ferromagneticmultilayers.
 35. The method of claim 28 wherein the forming of anon-magnetic spacer layer between a magnetic sense layer and a magneticstorage layer comprises forming a non-magnetic spacer layer between aferromagnetic storage layer and a ferromagnetic sense layer.
 36. Themethod of claim 28 wherein the forming of an antiferromagnetic layer inproximity to one of the magnetic storage layer and the magnetic senselayer comprises forming the antiferromagnetic layer between the magneticstorage layer and the non-magnetic spacer layer.
 37. The method of claim28 wherein the forming of an antiferromagnetic layer in proximity to oneof the magnetic storage layer and the magnetic sense layer comprisesforming the antiferromagnetic layer so that the magnetic storage layeris between the antiferromagnetic layer and the non-magnetic spacerlayer.
 38. The method of claim 28 wherein the forming of anantiferromagnetic layer in proximity to one of the magnetic storagelayer and the magnetic sense layer comprises: forming a firstantiferromagnetic layer in proximity to the magnetic storage layer; and,forming a second antiferromagnetic layer in proximity to the magneticsense layer.
 39. The method of claim 38 wherein the forming of anon-magnetic spacer layer between a magnetic sense layer and a magneticstorage layer comprises forming a non-magnetic spacer layer between aferromagnetic storage layer and a ferromagnetic sense layer.
 40. Themethod of claim 38 wherein the forming of a first antiferromagneticlayer in proximity to the magnetic storage layer comprises forming thefirst antiferromagnetic layer so that the storage layer is between thenon-magnetic spacer layer and the first antiferromagnetic layer, andwherein the forming of a second antiferromagnetic layer in proximity tothe magnetic sense layer comprises forming the second antiferromagneticlayer so that the sense layer is between the non-magnetic spacer layerand the second antiferromagnetic layer.
 41. The method of claim 38wherein the forming of a first antiferromagnetic layer in proximity tothe magnetic storage layer comprises forming the first antiferromagneticlayer so that the storage layer is between the non-magnetic spacer layerand the first antiferromagnetic layer, and wherein the forming of asecond antiferromagnetic layer in proximity to the magnetic sense layercomprises forming the second antiferromagnetic layer so that the secondantiferromagnetic layer is between the sense layer and the non-magneticspacer layer.
 42. The method of claim 38 wherein the forming of a firstantiferromagnetic layer in proximity to the magnetic storage layercomprises forming the first antiferromagnetic layer so that the firstantiferromagnetic layer is between the storage layer and thenon-magnetic spacer layer, and wherein the forming of a secondantiferromagnetic layer in proximity to the magnetic sense layercomprises forming the second antiferromagnetic layer so that the senselayer is between the second antiferromagnetic layer and the non-magneticspacer layer.
 43. The method of claim 38 wherein the forming of a firstantiferromagnetic layer in proximity to the magnetic storage layercomprises forming the first antiferromagnetic layer so that the firstantiferromagnetic layer is between the storage layer and thenon-magnetic spacer layer, and wherein the forming of a secondantiferromagnetic layer in proximity to the magnetic sense layercomprises forming the second antiferromagnetic layer so that the secondantiferromagnetic layer is between the sense layer and the non-magneticspacer layer.
 44. The method of claim 38 wherein the forming of a firstantiferromagnetic layer in proximity to the magnetic storage layercomprises forming first and second storage antiferromagnetic layers inproximity to the magnetic storage layer, wherein the forming of a secondantiferromagnetic layer in proximity to the magnetic sense layercomprises forming first and second sense antiferromagnetic layers inproximity to the magnetic sense layer, wherein the storage layer isbetween the first and second storage antiferromagnetic layers, whereinthe second storage antiferromagnetic layer is between the storage layerand the non-magnetic spacer layer, wherein the sense layer is betweenthe first and second sense antiferromagnetic layers, and wherein thesecond sense antiferromagnetic layer is between the sense layer and thenon-magnetic spacer layer.
 45. The method of claim 44 wherein the secondstorage antiferromagnetic layer is thinner that the first storageantiferromagnetic layer.
 46. The method of claim 44 wherein the secondsense antiferromagnetic layer is thinner that the first senseantiferromagnetic layer.
 47. The method of claim 46 wherein the secondstorage antiferromagnetic layer is thinner that the first storageantiferromagnetic layer.